In the field of non-impact printing, the most common types of printers have been the thermal printer and the ink jet printer. When the performance of a non-impact printer is compared with that of an impact printer, one of the problems in the non-impact machine has been obtaining and maintaining the required control of the printing operation. As is well-known, the impact printing operation depends upon the movement of impact members typically by reason of an electromechanical system which is believed to enable a more precise control of such impact members.
The advent of non-impact printing as in the case of thermal printing brought out the fact that the heating cycle must be controlled in a manner to obtain maximum repeated operations. Likewise, the control of ink jet printing must deal with the problem of rapid starting and stopping movement of the ink fluid from a supply of such fluid in order to minimize fluctuations thereof during print head reversal in direction of movement.
Representative prior art in the field of ink jet printing includes U.S. Pat. No. 3,747,120, issued to N. G. E. Stemme on July 17, 1973, which discloses an arrangement of writing mechanisms for applying droplets of ink in liquid form to a surface and wherein a chamber is divided into an inner portion and an outer portion with a channel connecting the portions. The chamber inner portion is provided with a piezoelectric device for producing short duration pressure increases in the fluid within the chamber and an intake or supply channel is connected with the chamber outer portion for transmission of the fluid through a discharge channel.
U.S. Pat. No. 3,946,398, issued to E. L. Kyser et al. on Mar. 23, 1976, discloses method and apparatus for recording with writing fluids and droplet projection means wherein a print head includes a piezoelectric crystal plate connected with a membrane and charged with a voltage pulse which causes the crystal plate and the membrane to bend and to produce pressure oscillations in an ink-filled liquid chamber of the print head. Upon each occurrence of a first maximum pressure in the liquid, an ink droplet is ejected through a nozzle and deposited on a record medium. In order to insure a safe release of the ink droplet at a sufficient initial speed, the crystal must be charged with a voltage pulse of sufficient height and width to bring about a respective maximum pressure in the liquid. A minimum pressure follows the maximum pressure in the liquid chamber and the chamber is again filled with ink so that by the following energization pulse of the crystal plate, a sufficient maximum pressure is produced which causes the next ink droplet to be ejected from the nozzle.
U.S. Pat. No. 4,074,284, issued to J. L. Dexter et al. on Feb. 14, 1978, discloses means for metering the flow of ink to the print head which includes a pressure sensor and a valve integrally incorporated into the print head. The pressure sensor detects changes in the fluid pressure in a pulse trap chamber and operates the valve to allow ink to flow to the pulse trap chamber upon the reduction of pressure below a predetermined level which is less than the maximum capillary pressure capable of being generated at the print head nozzles. The valve allows the maintenance of a substantially constant fluid pressure in the pulse trap chamber of the print head which feeds ink to the individual droplet ejection chambers. The pressure sensor and valve control system automatically compensates for the variations in the pressure of the high pressure source as the elastic force becomes less with removal of significant volumes of ink.
U.S. Pat. No. 4,125,845, issued to R. G. Stevenson on Nov. 14, 1978, discloses ink jet print head pressure and temperature control circuits wherein ink pressure within a pulse trap chamber is maintained within fixed limits by means of a first strain gauge connected for generating a signal proportional to the pressure of ink within the chamber and a second strain gauge utilized for temperature compensation of the pressure reading obtained from the first strain gauge. A valve operated by an electrical signal controls whether the ink passage into the chamber from an ink container is opened or closed.
U.S. application Ser. No. 159,414, filed June 13, 1980, which is a continuation-in-part application of Ser. No. 969,902, filed Dec. 15, 1978 by L. Bader et al., now abandoned, and assigned to the assignee hereof, discloses an ink jet control wherein a membrane is maintained by a drive element in a tensioned state for a delayed time such that negative or under-pressure resulting from release of the drive element occurs either after or prior to the minimum pressure following the maximum pressure. The system utilizes capillary forces and the relaxation of a piezoelectric crystal to supply ink to the reciprocating print head from a stationary reservoir which is open or vented to the atmosphere. The ink in the print head and the supply line is caused to be accelerated and decelerated during reverse or turnaround of the print head, thereby causing the ink to tend to be then forced out of the print head nozzle and/or air to be sucked into the print head through the nozzle. Either of these conditions may cause failure of the ink jet print head to operate properly.
While such ink movement problem can be controlled in one manner by supplying the ink to the print head at a relatively high pressure and using a sensor and a valve to control the ink pressure in the print head as per the disclosure in Dexter et al. U.S. Pat. No. 4,074,284 mentioned above, such technique involves the supplying of means to attain the high ink pressure in addition to the control valve and also an expensive sensing device.
Additionally, U.S. application Ser. No. 969,903, likewise filed Dec. 15, 1978 by L. Bader et al., now Pat. No. 4,223,323 issued Sept. 16, 1980, and assigned to the assignee hereof, discloses a plurality of printing elements connected by movable supply lines to an ink supply and disposed to maintain a small angle of ink flow when the print head moves from side to side. A secondary reservoir on the moving print head reduces fluctuations of the ink meniscus in the print head nozzle due to acceleration and deceleration of the print head by trapping a small volume of air in the supply line to partially dampen the motion of the fluid.